Photovoltaics is the field of technology and research related to the practical application of photovoltaic cells in producing electricity from solar radiation (sunlight). Photovoltaic cells are often electrically connected and encapsulated as a module (photovoltaic panel). Photovoltaic electricity generation employs solar photovoltaic panels typically containing a number of photovoltaic cells containing a photovoltaic material. Materials presently used for photovoltaics include monocrystalline silicon, polycrystalline silicon, amorphous silicon, cadmium telluride, and copper indium selenide/sulfide. When a photon is absorbed by a photovoltaic cell, it can produce an electron-hole pair. One of the electric charge carriers may reach the p-n junction and contribute to the current produced by the solar cell, or the carriers recombine with no net contribution to electric current, but generating heat. Furthermore, a photon with its energy (hv) below the band gap of the absorber material cannot generate a hole-electron pair, and so its energy is not converted to useful output and only generates heat if absorbed. For a photon with its energy (hv) above the band gap energy, only a fraction of the energy above the band gap can be converted to useful output. When a photon of greater energy is absorbed, the excess energy above the band gap is converted to kinetic energy of the carrier combination. The excess kinetic energy is converted to heat through phonon interactions as the kinetic energy of the carriers slowing to equilibrium velocity. Consequently, photovoltaic cells operate as quantum energy conversion devices with thermodynamic efficiency limit. Today's photovoltaic panels typically convert about 15% of the solar energy they capture from the sun into electricity, leaving 85% to be dissipated as heat. This creates a major thermal design challenge since every degree of temperature rise in the photovoltaic panels reduces the power produced by 0.5%. For example, a high quality monocrystalline silicon solar cell, at 25° C. cell temperature, may produce 0.60 volts open-circuit. The cell temperature in full sunlight, even with 25° C. air temperature, will probably be close to 45° C., reducing the open-circuit voltage to 0.55 volts per cell.
Therefore, a major design challenge for the manufacturers of photovoltaic panels is keeping them cool. Adding forced air cooling would add to the cost and maintenance requirements and consume a significant amount of energy; therefore, nearly all photovoltaic panels are cooled solely by natural convection. This explains why, presently, most commercial modules are constructed in such a way that air can flow under the photovoltaic panels in order to maximize convective cooling. However, in all those cases, the solar heat is wasted without any utilization. Therefore, any new approach that could utilize and remove the solar waste heat in a productive manner while generating photovoltaic electricity would be helpful to improving the overall system productivity and energy efficiency.
Desalination of seawater is another major challenge related to energy and sustainability on Earth. In many parts of the world, freshwater is in short supply. Salt is often quite expensive to remove from seawater, and salt content is an important factor in water use, i.e., potability. Currently, multi-stage flash distillation and reverse osmosis are the two major engineering processes for desalination of seawater. Both of the processes are energy intensive and discharge significant amounts of brine liquid into the environment, which is an environmental concern.
International Application No. PCT/US2009/034780 discloses a set of methods (1) on synthetic biology to create designer photosynthetic organisms (such as oxyphotobacteria, also known as blue-green algae) for photobiological production of advanced biofuels such as ethanol from carbon dioxide (CO2) and water (H2O) and (2) on a greenhouse distillation system technology to harvest the photobiologically produced ethanol from the ethanol-producing algal liquid mass culture.